Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C38: Ultracold Atoms: Superfluidity and Matter Wave Interferometry |
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Sponsoring Units: DAMOP Chair: Alexey Gorshkov, University of Maryland Room: 385 |
Monday, March 13, 2017 2:30PM - 2:42PM |
C38.00001: Controllable friction of dark solitons in Bose-Fermi mixtures Hilary Hurst, Dmitry Efimkin, Victor Galitski We study controllable friction in a system consisting of a dark soliton in a one-dimensional Bose gas and a non-interacting, degenerate Fermi gas. The fermions act as impurity atoms, not part of the original condensate, that scatter off of the soliton. We study semi-classical dynamics of the dark soliton by treating it as a particle with negative mass, and calculate its friction coefficient. Surprisingly, the amount of friction depends on the ratio of interspecies (impurity-condensate) to intraspecies (condensate-condensate) interaction strengths. By tuning this ratio, one can access a regime where the friction coefficient vanishes. We compare our results to experimental regimes and conclude that tunable friction has measurable physical consquences in experiments with Bose-Fermi mixtures. [Preview Abstract] |
Monday, March 13, 2017 2:42PM - 2:54PM |
C38.00002: Sonic Black Hole in multi-component Bose-Einstein condensate Sankalpa Ghosh, Priyam Das, Inderpreet Kaur Recently, a sonic Black Hole (sonic BH) configuration has been created experimentally in ultra cold atomic Bose Einstein Condensate (BEC) of Rubidium atoms, where instead of light it is sound (phonons), which cannot escape. Related Hawking radiation and entanglement between phonons were also studied. We consider such sonic BH configuration in a multi-component BEC under synthetic gauge fields. We examine the analogue space-time metric for such sonic BH, event horizon to find out their dependence on the intra- and inter-species interactions and the gauge field. The two-body correlation function between the phonons inside and outside the event horizon are also analysed. [Preview Abstract] |
Monday, March 13, 2017 2:54PM - 3:06PM |
C38.00003: Collective Modes in a Trapped Gas from Second-Order Hydrodynamics William Lewis, Paul Romatschke Navier-Stokes equations are often used to analyze collective oscillations and expansion dynamics of strongly interacting quantum gases. However, their use, for example, in precision determination of transport properties such as the ratio shear viscosity to entropy density ($\eta/s$) in strongly interacting Fermi gases problematic. Second-order hydrodynamics addresses this by promoting the viscous stress tensor to a hydrodynamic variable relaxing to the Navier-Stokes form on a timescale $\tau_\pi$. We derive frequencies, damping rates, and spatial structure of collective oscillations up to the decapole mode of a harmonically trapped gas in this framework. We find damping of higher-order modes (i.e. beyond quadrupolar) exhibits greater sensitivity to shear viscosity. Thus measurement of the hexapolar mode, for example, may lead to a stronger experimental constraint on $\eta/s$. Additionally, we find ``non-hydrodynamic" modes not contained in a Navier-Stokes description. We calculate excitation amplitudes of non-hydrodynamic modes demonstrating they should be observable. Non-hydrodynamic modes may have implications for the hydrodynamization timescale, the existence of quasi-particles, and universal transport behavior in strongly interacting quantum fluids. [Preview Abstract] |
Monday, March 13, 2017 3:06PM - 3:18PM |
C38.00004: A Geometric Theory of Fluctuations in Superfluid Hydrodynamics Aydin Keser, Victor Galitski We derive the "geometric theory of fluctuations," named after the analogy between general relativity and the hydrodynamic equations of superfluid flow, to compute the fluctuations in a superfluid and dissipation due to excitations. In this analogy, the superfluid component gives rise to a curved space-time whereas the normal component (excitations) plays the role of a matter field. We write a Langevin-type stochastic equation for the two fluid system and find the noise and dissipation in terms of the correlators of the covariant stress-energy operator. We examine the structure of fluctuations and dissipation in the stationary equilibrium (Minkowski) background and discuss possible implications of our findings for the hydrodynamic limit of condensed matter systems. [Preview Abstract] |
Monday, March 13, 2017 3:18PM - 3:30PM |
C38.00005: Amplitude Excitations in a Symmetry-Breaking Quantum Phase Transition Matthew Boguslawski, Bharath H M, Maryrose Barrios, Michael Chapman Quantum phase transitions (QPT) can be characterized using a local order parameter. In a symmetry-breaking phase transition, this order parameter spontaneously breaks one or more of the symmetries of the Hamiltonian while crossing the quantum critical point (QCP). A spin-1 Bose –Einstein condensate, in a single spatial mode, undergoes a QPT when the applied magnetic field is quenched through a critical value. The transverse spin component is an order parameter characterizing this QPT. It shares a U(1)×SO(2) symmetry with the Hamiltonian, but one of these two symmetries is broken when the system is quenched through the QCP. As a result, two massless, coupled phonon-magnon modes are present along with a single massive, or Higgs-like mode which has the form of amplitude excitations of the order parameter. Here, we experimentally characterize this phase transition and the resulting amplitude excitations by inducing coherent oscillation in the spin population [1]. We further use the amplitude oscillations to measure the energy gap between the ground state and the first excited state for different phases of the QPT. At the QCP, finite size effects lead to a non-zero gap, and our measurements are consistent with this prediction. \\ 1. T. M. Hoang et al, PNAS, 113, 34, 2016 [Preview Abstract] |
Monday, March 13, 2017 3:30PM - 3:42PM |
C38.00006: Simulating Infinite Vortex Lattices in Superfluids Luca Mingarelli, Eric Keaveny, Ryan Barnett We present an efficient framework to numerically treat infinite periodic vortex lattices in rotating superfluids described by the Gross-Pitaevskii theory. The commonly used split-step Fourier (SSF) spectral methods are inapplicable to such systems as the standard Fourier transform does not respect the boundary conditions mandated by the magnetic translation group. We present a generalisation of the SSF method which incorporates the correct boundary conditions by employing the so-called magnetic Fourier transform. We test the method and show that it reduces to known results in the lowest-Landau-level regime. Furthermore we extend such results to strong-interaction regimes and to the multicomponent case. [Preview Abstract] |
Monday, March 13, 2017 3:42PM - 3:54PM |
C38.00007: Producing flow in a ``racetrack'' Bose--Einstein condensate atomtronic circuit Ben Eller, Brennan Coheleach, Charles Clark, Mark Edwards We have studied the flow produced by stirring an ultracold atomtronic system consisting of a gaseous Bose--Einstein condensate (BEC) confined in a ``racetrack'' potential. The BEC is assumed to be strongly confined in a horizontal plane by a vertical harmonic trap and, within this plane, subjected to an arbitrary two--dimensional potential. The racetrack potential is made up of two straight parallel channels connected on both ends by semicircular channels of the same width and (energy) depth as the straightaways. We used the Gross--Pitaevskii equation to simulate the behavior of the BEC in this potential when stirred by rotating paddles of various shapes including ellipses and rectangles. The paddle energy height and rotation speed were also varied. As part of the study we endeavored to find stirring schedules that would lead to smooth flow of the BEC. In this way a ``complete'' atomtronic circuit with non--zero current could be produced. We found a rich variety of topological excitations were produced during the stirring. Here we report the type and number of such excitations and effect of racetrack shape on their behavior. [Preview Abstract] |
Monday, March 13, 2017 3:54PM - 4:06PM |
C38.00008: Precision measurement of ``Big G'' on the International Space Station Elizabeth Ashwood, Doga Murat Kurkcuoglu, Charles Clark, Mark Edwards Recent measurements of Newton's universal gravitational constant (``Big G'') using atom interferometric methods have increased the uncertainty in the value of this important fundamental constant\footnote{See, e.g., S.\ Schlamminger, {\em Nature} {\bf 510}, 478 (2014)}. One natural venue for performing a new atom interferometry measurement of Big G is the Cold Atom Laboratory to be deployed to the International Space Station (ISS) in 2017. We use simulation tools based on the Lagrangian Variational Methods (LVM) to simulate rapidly a variety of different atom--interferometry (AI) schemes that could be implemented in the CAL on the ISS. The atom chip present in the CAL is capable of producing potentials in H--trap, T--trap, and Z--trap configurations. We present simulation results for several candidate AI schemes running in various atom--chip potentials with a source mass present and absent. These AI schemes are designed to avoid errors in estimating Big G due to, among other things, shaking of the ISS and shot--to--shot variation of the number of atoms in the condensate. We provide an error budget and assess the feasibility of performing a precision measurement in the CAL. [Preview Abstract] |
Monday, March 13, 2017 4:06PM - 4:18PM |
C38.00009: Towards Entangled Atom Interferometry Kishor Kapale Atom interferometry is an indispensable tool for ultra-precise metrology of electric, magnetic, and gravitational fields. The resolution available in the standard atom interferometric schemes is dictated by the standard quantum limit and it scales as $1/\sqrt{N}$, where $N$ is the total number of atoms passing through the interferometer. One can, in principle, increase this resolution by a factor of $\sqrt{N}$ if one is able to employ entangled atoms as opposed to uncorrelated atoms to achieve a resolution that scales as $1/N$. This domain of interferometry is popularly known as Heisenberg-limited interferometry (HLI). There have been a tremendous amount of efforts carried out in the last decade or so towards attaining Heisenberg-limited interferometry with photons. It is natural to think about parallels for interferometry with entangled states of atoms. It is, however, extremely difficult to obtain entangled states of atoms suitable for atom interferometry. In this presentation, I intend to discuss the challenges and possible routes to developing entangled atom interferometry using tools of quantum optics that allow us precise control over atom-light interaction and possible applications of such schemes. [Preview Abstract] |
Monday, March 13, 2017 4:18PM - 4:30PM |
C38.00010: Concepts and technology development towards a platform for macroscopic quantum experiments in space Rainer Kaltenbaek Tremendous progress has been achieved in space technology over the last decade. This technological heritage promises enabling applications of quantum technology in space already now or in the near future. Heritage in laser and optical technologies from LISA Pathfinder comprises core technologies required for quantum optical experiments. Low-noise micro-thruster technology from GAIA allows achieving an impressive quality of microgravity, and passive radiative cooling approaches as in the James Webb Space Telescope may be adapted for achieving cryogenic temperatures. Developments like these have rendered space an increasingly attractive platform for quantum-enhanced sensing and for fundamental tests of physics using quantum technology. In particular, there already have been significant efforts towards ralizing atom interferometry and atomic clocks in space as well as efforts to harness space as an environment for fundamental tests of physics using quantum optomechanics and high-mass matter-wave interferometry. Here, we will present recent efforts in spacecraft design and technology development towards this latter goal in the context of the mission proposal MAQRO. [Preview Abstract] |
Monday, March 13, 2017 4:30PM - 4:42PM |
C38.00011: Physics of Hollow Bose-Einstein Condensates Karmela Padavic, Kuei Sun, Frances Yang, Courtney Lannert, Smitha Vishveshwara We study properties of BEC's in spherically symmetric traps that allow the possibility of deforming the condensate smoothly from a filled sphere to a hollow shell. The deformation undergoes a distinct change in topology in going from a filled condensate to one with a hollow region. We show that collective modes of BECs reflect such a change and the associated appearance of a new inner boundary. We show distinct non-monotonic behavior and a dip-like feature in spherically symmetric modes. High angular momentum modes are particularly sensitive to the topological change as they correspond to surface waves localized to boundaries; the appearance of a new boundary creates a redistribution of nodes and collective mode structure. The findings are not only relevant to various physical systems that have been discussed in the past in the context of condensate shells, such as shells in neutron stars and superfluid-Mott structures in optical lattices, but also to a new set of upcoming experiments in NASA's Cold Atomic Laboratory in which this very tuning between filled and hollow spheres is anticipated. [Preview Abstract] |
Monday, March 13, 2017 4:42PM - 4:54PM |
C38.00012: Quantum Breakup of Higher Order Bright Solitons Lincoln Carr, Christoph Weiss Semiclassical mean field theory in the form of the nonlinear Schrodinger equation (NLS) has had incredible success in modeling the dynamics of repulsive Bose-Einstein condensates (BECs): experimentally observed predictions range from dark solitons to skyrmions. A key prediction for attractive BECs is the bright soliton. An order-two soliton can be produced in a BEC simply by increasing the interaction strength by a factor of four, via a Feshbach resonance. The NLS is exactly solvable in this case and predicts a beautiful time-periodic dynamical pattern. Using matrix-product state methods, we show that such far-from-equilibrium higher order bright solitons exhibit quantum depletion and in fact break up rapidly in the more complete underlying quantum theory. Such break-up presents a smoking gun signal for emergent phenomena in quantum systems that do not have a semiclassical limit, and are therefore truly quantum in nature at macroscopic scales. They also indicate a breakdown of semiclassical integrability at a more fundamental quantum level. [Preview Abstract] |
Monday, March 13, 2017 4:54PM - 5:06PM |
C38.00013: Charge transfer in collision of H$^{+}$ with Li(1s$^{2}$2s,2p$_{z})$: TD-MADNESS approach. F. Javier Dominguez, Predrag S. Krstic We study state-resolved charge transfer processes for H$+$ collisions with atomic neutral lithium, in its ground and first excited state, in range from 1 to 25 keV/amu. We solve numerically the time-dependent Schrodinger equation (TDSE), using TD-MADNESS, Time-Dependent version of the Multiresolution Adaptive Numerical Environment for Scientific Simulation [1]. An advantage of the MADNESS is that the desired local accuracy is input parameter to the calculation and the method adapts the multiresolution representation of the wavelets to obtain this accuracy. By working with the numerical mesh which adapts to the gradient of the potential, quite large numerical boxes can be used within realistic computing times. The large size numerical box in MADNESS enables accurate representations of the Rydberg states and continuum, usually a problem in other TDSE methods. The time evolution is modeled by the Chin-Chen representation of the evolution operator [2]. The atomic Li target is modeled by frozen-core pseudo-potential while the ion projectile follows a straight line trajectory. We report new benchmark data for charge transfer cross section to n$=$2, and 3 states of H from 1s$^{2}$2s and 1s$^{2}$2p$_{z}$ of Li. Available theoretical and experimental data in the literature are in reasonable agreement with our results [3]. [1] R. J. Harrison et al., J. Chem. Phys. 121, 11587 (2004). [2] F. J. Dominguez et al., Adv. Quantum Chem. 71, 353 (2015) [3] F. J. Dominguez and P. S. Krstic, J. Phys. B 49, 195206 (2016). [Preview Abstract] |
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